Abrasive sheet containing a grain-size binder with wax particles

ABSTRACT

The loading of an abrasive belt with particles of a soft metal during grinding or polishing of the latter is sharply reduced, the amount of metal removed per unit time greatly increased, and the useful life of the belt improved if the abrasive grains on the belt are covered with an intimate mixture of a solid binder with finely dispersed wax particles.

United States Patent Lukowski Dec. 16, 1975 1 ABRASIVE SHEET CONTAININGA [56] References Cited GRAIN-SIZE BINDER WITH WAX UNITED STATES PATENTSPARTICLES 2,881,065 4/1959 Reuter 51/305 [75] Inventor: Heinz Lukowski,Wesseling, 2,899,290 8/19 Riegler 4 4 5l/305 Germany 3,102,010 8/1963Lang .1 51/298 3,195,993 7/1965 Gladstone 51/295 [73] Asstgnee:Feldmuhle Anlagenund 3,205,054 9/1965 Tucker 1 1 5l/298Produktionsgesellschaft mit 3,331,667 7/1967 Schnabel... 51/298beschrankter Haflung, 3,676,092 7/1972 Buell 51/298Duesseldorf-Oberkassel, Germany 1 Primary Examiner-Donald J .1 Arnold[22] Flled 1974 Attorney, Agent, or FirmHans Berman [21] App]. No.:447,789

- 57 ABSTRACT Foreign Application Priority Data The loading of anabrasive belt with particles of a soft Mar. 10,1973 Germany 2312052metal during grinding or polishing of the latter is sharply reduced, theamount of metal removed per [52] US. Cl. 51/295; 51/298; 51/301; unittime greatly increased, and the useful life of the 51/305; 51/306 beltimproved if the abrasive grains on the belt are [51] Int. Cl. B24D11/02; C08] 5/ 14 covered with an intimate mixture of a solid binder[58] Field of Search 51/295, 298, 305, 301, with finely dispersed waxparticles.

9 Claims, N0 Drawings ABRASIVE SHEET CONTAINING A GRAIN-SIZE BINDER WITHWAX PARTICLES This invention relates to abrasive sheet material, andparticularly to an improved abrasive sheet material suitable forfine-grinding and polishing soft, non-ferrous metals such as copper,aluminum, and their soft alloys.

The term abrasive sheet material, as employed herein, covers paper andfabric sheets and belts coated with abrasive grains which are bonded tothe fibrous, flexible base by a layer of binder material. When suchabrasive sheet material is employed for removing sur* face layers ofsoft, particularly non-ferrous metal, the metal tends to drag and toload the abrasive sheet, that is, particles of the soft metal tend toclog the interstices between the abrasive grains on the surface of theflexible base. It is impractical to remove the metal from the abrasivesheet, and it is not unusual to discard abrasive belts or flat sheetsbefore much of the abrasive material is lost from the base. The problemis of minor consequence in rough-grinding, but increases in importanceas the size of the abrasive particles decreases. This invention isconcerned primarily with improving abrasive sheet material in which theabrasive grains have a size smaller than 100 grit, but its advantagesare available, at least to some extent, in coarser abrasive sheets.

It has been usual practice to apply a greasy lubricant, such as tallow,to an abrasive belt, particularly when the belt travels at the high endof the usual grinding and polishing range of 5,000 to 10,000 ft./min.The improvement achieved is relatively modest, and it is necessarycontinuously to replenish the lubricant which is thrown from the belt bycentrifugal forces and contaminates the work area. The use of solidchloroparaffin lubricant, which has been proposed in US. Pat. No.3,676,092, overcomes some of the disadvantages of tallow, but the rateof material removal from a soft metal work piece is improved only byabout 50 percent.

Polytetrafluoroethylene has been proposed as a lubricant coating forabrasive material in US. Pat. No. 3,042,508, and has been shown toprovide greatly improved grinding efficiency, but it is not practical toapply a continuous and coherent fluorocarbon layer to abrasive grains ona fibrous substrate such as paper or cloth because the fluorocarbonlayer must be consolidated at temperatures well beyond the decompositiontemperature of the usual flexible base materials.

Only minor improvements in grinding efi'lciency were achieved by themethod of US. Pat. No. 2,893,854 in which granular abrasive is coatedwith a layer of ethyl cellulose, metal soaps, and fillers. The addedlayer can retard loading of the abrasive grains with soft metalparticles only for a very limited time.

The object of the invention is the provision of an improved grinding orpolishing material of the type in which one of the major faces of aflexible base of sheet material carries a layer of binder material, anda multiplicity of abrasive grains are secured to the base by the bindermaterial.

The improved grinding or polishing material of the invention includes anexposed covering layer covering the abrasive grains and essentiallyconsisting of an intimate mixture of a second binder material and wax.The wax is present in the mixture in the form of particles having anaverage size of less than 500 microns, and the second binder material issolid and shape-retaining at least at 25C when traveling at 10,000ft/min. in a circular path of 4 inch diameter. The weight ratio betweenthe second binder material to the wax in the mixture is between 1:5 and2:1, and preferably between 1:1 and 2:3.

The term wax is employed herein according to modern usage, as defined byl-llackhs Chemical Dictionary (McGraw-l-lill Book Company, New York,1969), to encompass substances characterized by a crystalline tomicrocrystalline structure, the capacity of acquiring gloss when rubbed,the capacity to produce pastes or gels with suitable solvents or whenmixed with other waxes, a low viscosity at just about the melting point,and low solubility in solvents for fats at room temperature. A wax, forthe purpose of this invention, thus may be a mineral wax, an animal orvegetal wax, or a synthetic wax. Beeswax, carnauba wax, ouricuri wax,paraffin, ceresin, polyolefin waxes, and amide waxes are merelyrepresentative of suitable waxes.

The binder materials employed for securing the abrasive grains to theflexible base are conventional and include synthetic resin compositions,but also water soluble glue, such as hide glue. The second bindermaterial which is mixed with the wax in the covering layer must bestrong enough to prevent loss of wax by centrifugal force generatedtypically when an abrasive belt travels at 10,000 ft./min. in acircularly arcuate path about a pulley 4 inches in diameter, but greaterstrength, of course, is desirable as far as it is consistent with thenecessary flexibility of the abrasive sheet material.

Binder materials combined with the wax particles in the covering layerthus may be synthetic resin compositions including phenolic, urea,epoxy, polyester, polyurethane, and alkyd resins, but. also watersoluble glue.

It is normally most advantageous to hold the weight ratio of bindermaterial and wax in the covering layer between 1:1 and 2:3. Noadvantages can be achieved by deviating from this ratio. When the bindermaterial amounts to less than about 16 percent of the mixture (a ratioof 1:5), the adhesion of the covering layer to the abrasive grains isnormally too small, and the covering layer is released from the grindingsheet in a relatively short time. When the binder material exceeds about66 percent of the mixture (a ratio of 2:1), the improvement achieved bythe presence of the wax is normally unsatisfactory. As a general rule,and particularly when using amide waxes, the best results are achievedat an approximate ratio of one part binder to 1.35 part wax.

The preferred amide waxes are derivatives of ethylenediamine in whichtwo acyl radicals of fatty acids, particularly of stearic, palmitic, andoleic acid, are attached to at least one amine nitrogen, and morespecifically the distearoylethylenediamines. The commercial productswhich are nominally distearoylethylenediamines are mixtures of the N,N-and N,N'-isomers, and may contain minor amounts of impurities. Thespecific location of the acyl groups and the presence of minor amountsof impurities have not been found significantly to affect theperformance of the amide waxes.

The effectiveness of a covering layer in the abrasive sheet material ofthe invention is not impaired by the presence of a pulverulent,inorganic or organic filler which is softer than the abrasive grainsemployed if it does not amount to more than 60 percent of the weight ofthe covering layer. Calcium carbonate is typical of inexpensive fillermaterials readily available.

The weight of the covering layer may vary between 5 and 1,000 g/m andwill be selected according to the mesh or grit of the abrasive grains.Coarse abrasive generally requires a heavier covering layer than finerabrasive grain. For abrasive grains smaller than 100 grit, which benefitmost from the improvement of this invention, a covering layer of 5 tog/m is adequate.

The greatest improvement in grinding performance as compared to abrasivematerial without a wax-bearing covering layer has been achieved so farin an abrasive belt in which the grains of abrasive material are bondedto the fibrous base by means of water soluble animal glue (hide glue),the covering layer consists of amide wax and a cured epoxy resin, and alayer of cured phenol-formaldehyde resin is interposed between thegrains and the exposed covering layer.

The following Examples further illustrate the invention:

EXAMPLE 1 An endless belt of cotton twill having two major faces 50 mmwide and 3,500 mm long was coated on a roller coater with a commercial,water-bearing, A-stage phenol formaldehyde resin composition having anominal viscosity of 800 cp to 1,000 cp, a pH of 8.0 to 9.0, and adensity of about 1.25 at C. The resin composition was capable ofconversion to the B-stage in about 5 minutes at 120C without significantloss of formaldehyde;

The coated base of textile sheet material was covered with 120-gritemery grains from an electrostatic spray gun, and the abrasive grainswere bonded to the base by heating to 90C until the resin layersolidified. The grains then were covered with a surface layer preparedby dispersing 10 parts micronized amide wax and 4 parts calciumcarbonate powder in 20 parts of another commercial, A-stage phenolformaldehyde composition and depositing the mixture by means of a rollercoater, all parts herein being by weight unless stated otherwise.

The amide wax was Hoechst Wax C, a commercial product essentiallyconsisting of di-octadecanoylethylenediamine, the stearoyl groups beingbound to the nitrogen atoms of the diamine. The wax employed had anominal dropping point of 139 to 144C, an acid number of 3 7, asaponification number of 3 10, a density of 0.99 1.01 at 20C, and wasfree from measurable amounts of ash.

The A-stage phenolic resin employed as a binder material in the coveringor surface layer had nominal properties of 900 to 1,100 cp viscosity, apH of 8.0 to 8.5, a density of 1.26 at 20C, and it converted to theB-stage in about 10 minutes at 120C.

The laminar belt structure so obtained was cured in an oven at atemperature gradually raised to 120C, and held at 120C for 2 hours.

Additional belts were prepared from otherwise the same materialsemploying 220, 320, and 400 grit emery. A second set of four abrasivebelts was prepared for comparison purposes without the amide wax underotherwise identical conditions.

The weight ratio of first binder layer, abrasive grains, and coveringlayer were as shown in Table 1 which also lists weight ratios forabrasive grit not employed in this Example, but referred to hereinbelow.The Table applies to all Examples unless stated otherwise.

TABLE 1 Weight, g/m

Grit 1st Binder Abrasive Coverq Layer TABLE 2 Weight loss, g Grit Withwax Without wax EXAMPLE 2 A fabric belt of the type and dimensionsdescribed in Example 1 was coated with hide glue in a conventionalmanner and covered with grit emery grains as in Example 1. After dryingof the glue layer, a phenolic resin layer was deposited and was cured asin Example 1. The weight of this layer, when cured, was 40 g/cm TheA-stage phenol-formaldehyde composition employed was identical with thatused as a first binder between the abrasive grains and the base inExample 1.

The belt so prepared was tested as described in Example 1. It removed 30g aluminum from a test body in the standard testing period of 60minutes, and did not contain wax in a covering layer.

EXAMPLE 3 A belt prepared as in Example 2 was further coated with acovering layer prepared by intimately mixing 134 parts micronizedHoechst Wax C with 100 parts of a liquid epoxy resin compositioncontaining a hardener, and curing the covering layer.

The amount of aluminum removed by the modified belt from a test bodyunder conditions otherwise identical with those used in Example 2increased from 30 g to 227 g.

EXAMPLE 4 In the otherwise unchanged procedure of Example 3, Hoechst WaxC was replaced by an equal amount of an amide wax commercially availableas Glockem Wax D2S, chemically closely similar to Hoechst Wax C, andhaving a similar range of physical properties including a dropping pointof 142 147C, an acid number of 2 6, a saponification number of less than6, a density of 0.997 at 20C, and an ash content of 0.018 percent.

The belt so prepared removed 207 g aluminum from the test body.

EXAMPLE 5 It removed 207 g aluminum from the standard test body.

EXAMPLE 6 134 Parts paraffin was dissolved in benzene, and the benzenesolution was mixed with the liquid, catalyzed epoxy resin compositionemployed in Examples 3 and 4 by means of a high speed mixer which causedsmall paraffin particles to be uniformly dispersed in the resincomposition. The mixture so obtained was applied to a belt prepared asin Example 2, and the coated belt was stored until the resin was fullycured.

214 g Aluminum were removed by the cured belt from the standard aluminumbody in the grinding test described in Example 1.

When polypropylene wax was substituted for the paraffin, the belt wascapable of removing 162 g aluminum in the standard test.

EXAMPLE 7 A belt prepared as in Example 2 was coated with a coveringlayer initially consisting of an intimate mixture of 100 parts liquidepoxy resin composition containing a hardener and identical with thecomposition employed in Examples 3 and 4, 134 parts micronized HoechstWax C, and parts calcium carbonate powder.

The belt, when tested after complete cure of the resin, removed 24] galuminum from the test body. The improvement apparently due to thepresence of the filler material cannot be fully explained at this time.

When the amount of calcium carbonate was increased to 50 parts underotherwise unchanged conditions, the amount of removed aluminum wasreduced to 227 g, and a further reduction to 216 g occurred when thecalcium carbonate was further increased to 200 parts.

EXAMPLE 8 In a procedure otherwise unchanged from that of Example 7, thecalcium carbonate in the covering layer was replaced by 10 partspowdered cryolite (Na AlF The aluminum removed in the standard test ofExample 1 amounted to 231 g.

When the cryolite was increased to 50 parts, aluminum removal remainedapproximately unchanged at 228 g. It was reduced to 208 g when thecryolite was further increased to 150 parts.

EXAMPLE 9 The procedure of Example 2 was repeated using 320 grit emeryand a correspondingly reduced layer of glue (see Table 1). The thicknessof the phenolic resin layer applied over the abrasive grains also wasreduced to g/m The belt so prepared removed 4 g aluminum from the testbody in the standard grinding test of Example 1.

Application of a covering layer of epoxy resin composition and amidewax, as in Example 3, improved the test result to 36 g aluminum.

EXAMPLE 10 A twill belt was coated with a first binder layer of A-stagephenolic resin composition and with grit emery as in Example 1. Afterpartial curing of the first binder layer, the grit was covered withenough additional A-stage phenol-formaldehyde resin to make the secondor intermediate layer 50 g/m after curing. As a covering or surfacelayer, the: mixture of epoxy resin composition and amide wax describedin Example ,3 was applied. A control sample lacking the covering layerwas also prepared.

Y A test block of structural steel having a tensile strength between 37and 45 kplmm a carbon content of less than 0.20 percent, a phosphorouscontent of less than 0.06 percent, and a sulfur content of less than0.05 percent was ground on a commercial belt grinder at a speed of 6,000ft./min. and at a pressure of 6 kg by means of the two belts. Thecontrol belt removed 306 g steel and lost 3.5 g of its abrasive grainsafter 30 minutes grinding. The belt according to the invention removedonly 269 g steel and lost 6.1 g abrasive material, being thus clearlyinferior to the control.

When an aluminum test body (99 percent Al) was ground on the samemachine at a pressure of 4 kg with the two belts, the control removedonly 56 g aluminum and lost 2.2 g abrasive, while the belt according tothe invention removed 166 g aluminum, losing 6.6 g abrasive grains.

Additional belts were prepared from 220 grit emery with correspondinglyreduced thicknesses of bonding material and covering layer, and employedin tests on bodies of the above-mentioned mild structural steel, anaustenitic stainless steel, commercial aluminum (99 percent Al), brass(58 percent Cu), phosphorbronze, copper, melamine formaldehyde resin,and nylon 6. The belt according to this invention was superior to thecontrol belt in grinding aluminum, copper, nylon, stainless steel,melamin resin, and brass, in that order, and inferior to the controlbelt on the harder metal of the structural steel and phosphorbronze.

These results could be duplicated, at least in a qualitative manner,using other commercial belt grinders at different contact pressures,belt speeds, abrasive grits. Substitution of paper as a base materialdid not have a significant effect on the results. Limited tests withother abrasives (silicon carbide, quartz sand) showed that the nature ofthe abrasive has no bearing on the advantages of the abrasive sheetmaterial of the invention.

It should be understood, of course, that the foregoing disclosurerelates only to preferred embodiments of the invention, and that it isintended to cover all changes and modifications of the Examples of theinvention herein chosen for the purpose of the disclosure which do notconstitute departures from the spirit and scope of the invention setforth in the appended claims.

What is claimed is:

1. In a grinding or polishing material having a flexible base of sheetmaterial, a layer of a first binder material on one of the major facesof said base, and a multiplicity of abrasive grains secured by saidbinder material to said base, the improvement which comprises a coveringlayer covering said grains and said first binder material andessentially consisting of an intimate mixture of a second bindermaterial and a wax, said wax being pre= ent in said mixture in the formof particles having an average size of less than 500' microns, saidsecofl binder material being solid and shape-retaining at 25 whentraveling at 10,000 ft./min. in a circular arc of 4 inch diameter, theweight ratio of said second binder material to said wax in said mixturebeing between 1:5 and 2:1, said second binder material securing saidparticles to said grains, said first binder material, and said base,said binder materials being members of the group consisting of phenolformaldehyde resin, urea formaldehyde resin, epoxy resin, polyesterresin, polyurethane resin, alkyd resin, and water soluble glue.

2. In a material as set forth in claim 1, the weight ratio of saidsecond binder material to said wax being between 1:1 and 2:3.

3. In a material as set forth in claim 2, said covering layer containingup to 60 percent by weight of a solid, particulate filler having ahardness substantially smaller than the hardness of said grains.

4. In a material as set forth in claim 1, a layer of curedphenol-formaldehyde resin composition interposed between said grains andsaid covering layer.

5. In a material as set forth in claim 4, said first binder materialessentially consisting of water-soluble glue, said Second bindermaterial being a cured epoxy resin composition, and said wax is an amideof a fatty acid.

6. In a material as set forth in claim 1, the size of said abrasivegrains being smaller than 100 grit.

7, In a material as set forth in claim 1, said wax beingdistea'roylethylenediamine.

8. In a material as set forth in claim 2, said second binder materialbeing a cured epoxy or phenol formaldehyde resin, and said wax being anamide of a fatty acid.

9. In a material as set forth in claim 1 and said wax being a memberselected from the group consisting of beeswax, carnauba wax, ouricouriwax, paraffin, ceresin, polyolefin wax, and amide wax.

1. IN A GRINDING OR POLISHING MATERIAL HAVING A FLEXIBLE BASE OF SHEETMATERIAL, A LAYER OF A FIRST BINDER MATERIAL ON ONE OF THE MAJOR FACESOF SAID BASE, AND A MULTIPLICITY OF ABRASIVE GRAINS SECURED BY SAIDBINDER MATERIAL TO SAID BASE, THE IMPROVEMENT WHICH COMPRISES A COVERINGLAYER COVERING SAID GRAINS AND SAID FIRST BINDER MATERIAL ESSENTIALLYCONSISTING OF AN INTIMATE MIXTURE OF A SECOND BINDER MATERIAL AND A EAXSAID WAX BEING PRESENT IN SAID MIXTURE IN THE FORM OF PARTICLES HAVINGAN AVERAGE SIZE OF LESS THAN 500 MICRONS, SAID SECOND BINDER MATERIALBEING SOLID AND SHAPE-RETAINING AT 25*C WHEN TRAVELING AT 10,000FT/MIN.IN A CIRCULAR ARC OF 4 INCH DIAMETER, THE WEIGHT RATIO OF SAID SECONDBINDER MATERIAL TO SAID WAX IN SAID MIXTURE BEING BETWEEN 1:5 AND 2:1,SAID SECOND BINDER MATERIAL SECURING SAID PARTICLES TO SAID GRAINS, SAIDFIRST BINDE MATERIAL, AND SAID BASE, SAID BINDER MATERIALS BEING MEMBERSOF THE GROUP CONSISTING OF PHENOL FORMALDEHYDE RESIN, UREA FORMALDEHYDERESIN, EXPOY RESIN, POLYESTER RESIN, POLYURETHANE RESIN, ALKYD RESIN ANDWATER SOLUBLE GLUE.
 2. In a material as set forth in claim 1, the weightratio of said second binder material to said wax being between 1:1 and2:
 3. 3. In a material as set forth in claim 2, said covering layercontaining up to 60 percent by weight of a solid, particulate fillerhaving a hardness substantially smaller than the hardness of saidgrains.
 4. In a material as set forth in claim 1, a layer of curedphenol-formaldehyde resin composition interposed between said grains andsaid covering layer.
 5. In a material as set forth in claim 4, saidfirst binder material essentially consisting of water-soluble glue, saidsecond binder material being a cured epoxy resin composition, and saidwax is an amide of a fatty acid.
 6. In a material as set forth in claim1, the size of said abrasive grains being smaller than 100 grit.
 7. In amaterial as set forth in claim 1, said wax beingdistearoylethylenediamine.
 8. In a material as set forth in claim 2,said second binder material being a cured epoxy or phenol formaldehyderesin, and said wax being an amide of a fatty acid.
 9. In a material asset forth in claim 1 and said wax being a member selected from the groupconsisting of beeswax, carnauba wax, ouricouri wax, paraffin, ceresin,polyolefin wax, and amide wax.